Linked Lists

[xGTx]

Is it always like

SetLength(mTile[X, Y].Animation.Frames, High(mTile[X, Y].Animation.Frames)+2);

or does it depend on the sizeof(frames) ?

[Harry Hunt]

Don't use SizeOf in this context, use Length. SizeOf will return the Byte-Size of the pointer which is always 4 bytes. Length will return the number of elements in a dynamic array. To append an element to a dynamic array, do this:

SetLength(Frames, Length(Frames) + 1);
Frame[Length(Frames) - 1].Color := clGreen;

[xGTx]

Doesn't High() do it?

[Harry Hunt]

yeah, high() will do it, too

[xGTx]

Whats the difference between the output of High() and Length() ?

And this is acting very strange: (giving me range check error after like 3 iterations of this functions)

[pascal]SetLength(mTile[X, Y].Animation.Frames, Length(mTile[X, Y].Animation.Frames)+1);
mTile[X, Y].Animation.Frames[Length(mTile[X, Y].Animation.Frames)-1].TileIndex := frmMain.cTileID - (Trunc(frmMain.cTileID div 112) * 112);
mTile[X, Y].Animation.Frames[Length(mTile[X, Y].Animation.Frames)-1].TextureIndex := Trunc(frmMain.cTileID div 112);[/pascal]

[Useless Hacker]

Whats the difference between the output of High() and Length() ?

Length() returns the number of elements in an array (or the length of a string); High() returns the index of the last element in an array - usually this is Length()-1. There is also the Low() function, which returns the index of the first element in an array, and will in nearly every case be 0. It is, however, possible in Delphi to have static arrays that do not start at index 0, for example if you are using an enum as the index.

[cairnswm]

I think Dynamic arrays always start at 0.

[WILL]

I think Dynamic arrays always start at 0.

Thats exactly right, they always start at 0. When you
[pascal]var dArray : Array of Char;
SetLength(dArray, 20);[/pascal]
dArray will be from 0 to 19. Then
[pascal]a := Length(dArray);
// a = 20

b := High(dArray);
// b = 19

c := Low(dArray);
// c = 0[/pascal]

Just be careful how you use Dynamic arrays within other data structures. The effects can be a bit unpredictable. Misuse of them is what would result in a 'memory leak' in your program. Dynamic Arrays within dynamic arrays is also highly UNrecommended(if your program will even function properly). You re pretty much dealing with memory management when you play with them.

[xGTx]

Thanks alot guys. Now removing from a dynamic array is


[pascal]
SetLength(Frames, High(Frames)-1);
[/pascal]

Since high() is the actuall number of elements in the array and -1 would drop it down 1. Correct?

[Harry Hunt]

No, High is the last index of the array and Length is the count.
To delete the last item do this

[pascal]SetLength(MyArray, Length(MyArray) - 1);[/pascal]

or this

[pascal]SetLength(MyArray, High(MyArray));[/pascal]